<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .app{
            width: 100px;
            height: 100px;
            border: 1px solid #ccc;
            position: relative;
        }
        .box{
            width: 50px;
            height: 50px;
            position:absolute;
            top: 10px;
            background-color: pink;
        }
        .test{
            /* position:absolute; */
            top: 10px;
            width: 20px;
            height: 20px;
            background-color: black;
        }
    </style>
</head>
<body>
    <div class="app">
        <div class="box">
            <div class="test"></div>
        </div>
    </div>
</body>
</html>